As a fluorinated diene compound having two carbon—carbon unsaturated double bonds (hereinafter referred to as unsaturated bonds), CF2═CF(CF2)kOCF═CF2 (wherein k is an integer of from 1 to 3) is known (JP-A-1-143843). By cyclopolymerization of this compound, it is possible to obtain an amorphous polymer. Such a polymer has high elastic modulus, yield and breaking elongation and is tough and excellent also in impact resistance. Further, it has high transparency, and it is useful for an optical material for e.g. optical fibers and optical waveguides. However, the optical material employing this polymer has a low glass transition temperature (Tg) and thus has a drawback that the optical characteristics are likely to change when it is used at a high temperature for a long period of time. Accordingly, it is desired to develop a material having a higher Tg.
It is an object of the present invention to provide a novel polymer which not only maintains the mechanical properties which the above-mentioned amorphous polymer has, but also has a higher glass transition temperature, so that it can be an optical resin material having a low refractive index and being excellent in heat resistance, and a novel fluorinated diene compound having two unsaturated bonds, which presents such a polymer. Further, it is an object of the present invention to provide a high performance light transmitter and a plastic optical fiber, which have a low refractive index and excellent heat resistance.